fixes handling of audiofiles.

[lethliel]

Now in the __init__.py of the projects a audiofile can be given to the Rendertask:

For example:

queue.put(Rendertask(
    infile = 'intro.svg',
    audiofile = 'intro.mpg',
    outfile = str(event['id'])+".ts",
    sequence = introFrames,
    parameters = {
        '$ID': event['id'],
        '$TITLE': event['title'],
        '$SUBTITLE': event['subtitle'],
        '$SPEAKER': event['personnames']
         }
    ))